This invention relates to the pipe diameter to orifice diameter (Beta-Ratio) in the measurement of fluids using concentric orifice as the primary element.
The American Gas Association's report Number Three set the recommended orifice to pipe diameter ratio (d/D="B") using "Flange Taps" to be between 0.15 and 0.70 (Ref.,AGA Report 3, Paragraph 2.2,6). The report states that ratios as low as 0.10 may be used, but the flow constants, Fb, for these extreme values of "B" are subject to higher tolerances and should be avoided.
At this point the need arises to modify the metering station. It has been the common practice to replace the metering tube with one of a smaller diameter to reestablish a workable Beta Ratio range. I believe that my invention will provide a more practical and useful means of accomplishing this modification. The problem this invention solves is explained in the following paragraphs.
As the fluid flow across the orifice meter decreases, a smaller orifice must be installed so that a differential in pressure is maintained at a recording instrument (such as one described in U.S. Pat. No. 2,365,573, to J. B. McGay). If the fluid flow drops to the point that installation of a smaller orifice exceeds the recommended Beta Ratio, some corrective action must be taken if accurate measurement of the fluid is to be maintained.
An example of such a situation is a producing gas field that is experiencing a dropping demand for its product. When the fluid flow in its distribution system is curtailed, the flow from wells delivering gas into the system is reduced, slowing the fluid flow across its numerous metering stations, thereby necessitating the installation of smaller orifices. The flow from marginal wells in the system can no longer be accurately measured.
(As an example: A 4" metering tube that requires a 3/8" orifice ((Beta-Ratio 0.09)) to produce a recordable differential pressure but is below AGA recommendations of 0.15 Beta-Ratio). The choice of corrective action has been limited to replacing the meter tube with one of a smaller diameter (A 2" metering tube with a 3/8" orifice ((Beta-Ratio 0.18). In a field with many low pressure wells in its system, this solution is a very expensive undertaking.